Kinematic vorticity analysis as a microtectonic gauge for dextral transpression along Wadi Fatima Shear Zone in western Arabian Shield
摘要
The Wadi Fatima Shear Zone is characterised by the basement complex, which comprises an igneous/metamorphic group with transpressive structures that are syn-accretionary. The basement rocks are unconformably covered by post-amalgamation volcano-sedimentary rocks and display thrust-related structure and post-accretionary thrusting. The present work investigates the tectonics and structural evolution of the Wadi Fatima Shear Zone (WFSZ). It studied the mineralogy of sheared rocks and used the kinematic vorticity analysis to explain the tectonic movement in the WFSZ. In the present work, we used Passchier and RGN techniques. Similar patterns of deformation can be seen in the Fatima area of the western Arabian Shield. Porphyroclasts in high-temperature mylonites were analysed for vorticity analysis. When combined with the strain data, the kinematic vorticity (Wm) for the schist, amphibolite and gneiss rocks in the Wadi Fatima area ranges from 0.66 to 0.86, indicating dominance of simple shear. It appears that the nappe structure was subjected to ductile strain through thrusting and that nappe stacking happened early after the underthrusting phase, possibly as a result of brittle imbrication. The subhorizontal foliation in the WFSZ and in surrounding lithologies was caused by a vertical shortening, which contributed to the accumulation of ductile strain through thrusting rather than only shear.